In the manufacture of patterned devices such as semiconductor chips and chip carriers the steps of etching different layers which constitute the finished product are among the most critical and crucial steps involved.
In semiconductor manufacturing, optical lithography has been the main stream approach to pattern semiconductor devices. In typical prior art lithography processes, UV light is projected onto a silicon wafer coated with a layer of photosensitive resist through a mask that defines a particular circuitry pattern. Exposure to UV light, followed by subsequent baking, induces a photochemical reaction which changes the solubility of the exposed regions of the photosensitive resist. Thereafter, an appropriate developer, typically an aqueous base solution, is used to selectively remove the resist either in the exposed regions (positive-tone resists) or, in the unexposed region (negative-tone resists). The pattern thus defined is then imprinted on the silicon wafer by etching away the regions that are not protected by the resist with a dry or wet etch process.
The current state-of-the-art optical lithography uses DUV irradiation at a wavelength of 248 nm to print features as small as 250 nm in volume semiconductor manufacturing. The continued drive for the miniaturization of semiconductor devices places increasingly stringent requirements for resist materials, including high resolution, wide process latitude, good profile control and excellent plasma etch resistance for image transfer to substrate. Several techniques for enhancing the resolution, such as reduced irradiation wavelength (from 248 nm to 193 nm), higher numerical aperture (NA) of the exposure systems, use of alternate masks or illumination conditions, and reduced resist film thickness are currently being pursued. However, each of these approaches to enhance resolution suffers from various tradeoffs in process latitude, subsequent substrate etching and cost. For example, increasing NA of the exposure tools also leads to a dramatic reduction in the depth of focus. The reduction in the resist film thickness results in the concomitant detrimental effect of decreased etch resistance of the resist film for substrate etching. This detrimental effect is exasperated by the phenomenon of etch induced micro-channel formation during substrate etch, effectively rendering the top 0.2-0.3 .mu.m resist film useless as an etch mask for substrate etching.
It would therefore be desirable to provide for enhanced resolution without experiencing drawbacks of the prior art.
Furthermore, bilayer imaging schemes have been suggested. In a bilayer imaging scheme, typically, images are first defined in a thin, usually 0.1-0.3 .mu.m thick, silicon containing resist with a wet process on a relatively thick high absorbing organic underlayer. The images thus defined are then transferred into the underlayer through a selective and highly anisotropic oxygen reactive ion etching (O.sub.2 RIE) where silicon in the top imaging layer is converted into nonvolatile silicon oxides, thus acting as an etch mask. To be effective as etch mask, the top imaging layer needs to contain sufficient silicon, usually greater than 10 wt %
The advantages of bilayer imaging over the conventional single layer imaging include higher resolution capability, wider process latitude, patterning high aspect ration features, and minimization of substrate contamination and thin film interference effects. Moreover, the thick organic underlayer offers superior substrate etch resistance. The bilayer imaging is most suitable for high NA exposure tools, imaging over substrate topography and patterning high aspect ratio patterns.
Various silicon-containing polymers have been used as polymer resins in the top imaging layer resists (see R. D. Miller and G. M. Wallraff, Advanced Materials for Optics and Electronics, p. 95 (1994)). One of the most widely used silicon-containing polymers is polysilsesquioxane. Both positive-tone and negative-tone resists have been developed using an aqueous base soluble polysilsesquioxane: poly(p-hydroxybenzylsilsesquioxane). For positive-tone bilayer resists, poly(p-hydroxybenzylsilsesquioxane) was modified with a diazo photoactive compound or an acid sensitive t-butyloxycarbonyl (t-BOC) for I-line and chemically amplified DUV lithography, respectively [U.S. Pat. No. 5,385,804, U.S. Pat. No. 5,422,223]. Positive-tone resists have also been developed by using dissolution inhibitors [U.S. Pat. N. 4,745,169]. For negative-tone bilayer resists, an azide functional group was chemically attached to poly(p-hydroxybenzylsilsesquioxane). Exposure of the azide functionalized poly(p-hydroxybenzylsilsesquioxane) caused crosslinking in the exposed regions. Thus, negative-tone images resulted. However, these bilayer resists suffer from inadequate resolution, low sensitivity, and poor resist profile in some cases due to high optical density.
In view of the state of prior art resists, it is desirable to develop new bilayer resists with high resolution, high sensitivity, and good profile control for patterning semiconductor circuities. In particular, new negative-tone silicon-containing resists are desirable since negative-tone resists generally offer advantages of better isolated feature resolution, good thermal stability, small isolated and dense feature bias.